1. Field of the Invention
The present invention relates to an imaging device and a method of manufacturing the same, and more particularly to an infrared ray detecting type imaging device (an infrared imaging device) and a method of manufacturing the same.
2. Description of the Related Art
An infrared imaging device is proposed, in which a bolometer film is formed on a semiconductor substrate on which a circuit including transistor and wiring and the like is formed. This device detects an infrared ray for each pixel by making use of change of a resistance value of the bolometer film depending on temperature, and reads the detected signal by way of the transistor. In the conventional infrared imaging device, first, a circuit portion including a transistor and a metal wiring such as an aluminum wiring is formed on a semiconductor substrate, and then a bolometer film is formed thereon.
In such an infrared imaging device, however, the process temperature when forming a bolometer film must be about 450° C. or less, preferably about 400° C. or less. If the process temperature is higher, the metal wiring such as an aluminum wiring deteriorates. Further, by heat treatment at high temperature of about 800° C. or more, the transistor characteristic also deteriorates. Conventional films such as vanadium oxide films can be formed at relatively low temperature, and there is no problem, but when a material requiring to be formed at high temperature is used as a bolometer film, the metal wiring and transistors deteriorate. Therefore, in the conventional infrared imaging device, materials usable for the bolometer film are limited.
Hitherto, moreover, there are undulations due to wiring steps and contact holes beneath the bolometer film since the metal wiring and the like are formed on a lower side of the bolometer film. At these positions of steps and contact holes, the bolometer film has crystal disturbance and grain boundary, which causes noise or characteristic deterioration.
Therefore, in the conventional infrared imaging device, since the bolometer film must be formed at a relatively low temperature, materials for the bolometer film are limited. Besides, by the undulations existing beneath the bolometer film, noise and characteristic deterioration are caused. It was hence difficult to obtain an infrared imaging device of high performance.